Vehicles may include cooling systems configured to reduce overheating of an engine by transferring the heat to ambient air. Therein, coolant is circulated through the engine block to remove heat from the engine, the heated coolant then circulated through a radiator to dissipate the heat. The cooling system may include various components such as a coolant reservoir coupled to the system for degassing and storing coolant. A pressurized reservoir that also serves to separate entrained air from the coolant is typically called a degas bottle. When the temperature of coolant anywhere in the system rises, thermal expansion of the coolant causes pressure to rise in the degas bottle as the trapped air volume reduces. Pressure relief can be achieved by releasing air from the degas bottle through a valve that is typically mounted in the fill cap. Then, when the temperature and pressure of coolant drops below atmospheric pressure in the degas bottle, air may be drawn back into the bottle through another valve that is often mounted in the fill cap.
If the coolant level in bottle is too low, the air volume will be too large to build sufficient pressure to prevent boiling and cavitation at the water pump inlet. At low fluid levels, the degas bottle will also no longer be able to separate air from the coolant and air can be drawn into the cooling system, again leading to poor cooling performance. If an overflow system is employed instead of an active degas system, a similar loss in cooling system performance can be realized when fluid levels are low.
Various approaches may be used to estimate fluid level in a reservoir. One example approach described by Murphy in U.S. Pat. No. 8,583,387 uses an ultrasonic fluid level sensor installed at the bottom of a reservoir to estimate a fluid level of the reservoir. However, the inventors herein have recognized that in such a cooling system, the dimensions of the coolant reservoir may vary based on the temperature of coolant contained in the reservoir. As a result, there may be inconsistencies in the estimated coolant level. Additionally, due to the location of the sensor at the bottom of the container, at low coolant levels, it may be unclear whether the fluid level in the reservoir is low or empty. Further still, it may be difficult to differentiate actual low coolant levels from incorrect coolant level estimation due to sensor degradation. In another example approach, described by Gordon et al in US 20130103284, the sensor is coupled to a coolant reservoir hose. One issue with such an approach is that the sensor can only detect the presence of coolant at that location in the circuit. Critical components of the power train may not be receiving coolant despite the presence of coolant in one of the coolant reservoir hoses, particularly if that hose is isolated from the cooling system by a valve (e.g., the engine thermostat hose). Further, while an indication of low coolant fluid level is received, engine temperature control may already be degraded due to substantial emptying of the coolant reservoir.
In one example, the above issues may be at least partly addressed by a method for a coolant system, comprising: receiving each of unprocessed, raw echo times and processed fluid level data from a sensor coupled to a vertical tube, the tube positioned external to and fluidically coupled to a coolant reservoir at each of a top and bottom region; and generating a fluid level estimate based on the raw echo times and vehicle sensor data during a first condition; and generating the fluid level estimate based on the processed data during a second condition. In this way, the coolant level may be updated based on a sufficient number of each of first order and second order echoes of pulses transmitted from the vertical standpipe.
As one example, an engine coolant system may include a vertical tube aligned with a coolant overflow reservoir, the tube housing an ultrasonic sensor. The vertical tube may be coupled to the coolant reservoir at each of a top and bottom location via hoses, coolant flowing between the tube and the reservoir via the hoses. The hoses may be connected such that a headspace is generated between the top of the fluid level in the vertical tube and the top of the tube. In addition, the hoses may be connected such that the top of the vertical tube is arranged at a lower height than the top of the coolant reservoir, thereby allowing the sensor to more reliably estimate the fluid level in the reservoir and distinguish between low and empty coolant level states. The sensor, positioned inside a recess at the bottom of the vertical tube, may transmit a signal to the top of the vertical tube, an echo of the signal being received at the sensor after being reflected off the top of the tube. The signal may be transmitted periodically and based on an average echo time (which is the time elapsed between the signal being transmitted and an echo of the signal being received), the coolant level in the vertical tube may be estimated. This estimate may then be used to infer the coolant level in the reservoir. As one example, after a measurement period has elapsed, the engine controller may receive a sensor-processed coolant level, a total number of received echoes, a number of echoes with qualified echo times, first and second-order echo times for each emitted pulse in the measurement period, and temperatures of the sensor circuit board and coolant at the piezoelectric element of the sensor. If the number of qualified echo times is above a threshold number, the sensor-processed coolant level may be used. If the number of qualified echo times is below the threshold number, a coolant level may be calculated from raw first-order echo times. If this calculation does not result in a valid coolant level, a flag may be activated to indicate that there is not a valid coolant level reading for the measurement period, and the coolant level may not be updated.
In this way, an accuracy and reliability of determining a coolant level of a coolant overflow reservoir can be increased. By inferring the coolant level of the reservoir based on an estimated coolant level of a standpipe coupled to the reservoir, inaccuracies in coolant level estimation due to distortion of an in-tank sensor output during thermal fluctuations, or vehicle motion, is reduced. By enabling each of echo time raw data and processed data to be available for coolant level estimation, a controller maybe allowed to select data based on the number and output of first-order and second-order echoes. As such this increases the number of reliable data points that are used in coolant level estimation, improving the reliability of the generated result. By relying on an ultrasonic sensor and the local processor to estimate the coolant level of the standpipe based on raw and processed echo times, coolant level estimation can be expedited. Overall, engine overheating due to inaccurate coolant level estimation can be reduced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.